The Collaborative International Dictionary of English v.0.48:

Unwonted \Un*wont"ed\ ([u^]n*w[u^]nt"[e^]d), a.
   1. Not wonted; unaccustomed; unused; not made familiar by
      practice; as, a child unwonted to strangers. --Milton.
      [1913 Webster]

   2. Uncommon; unusual; infrequent; rare; as, unwonted changes.
      "Unwonted lights." --Byron.
      [1913 Webster] -- Un*wont"ed*ly, adv. --
      Un*wont"ed*ness, n.
      [1913 Webster]

WordNet (r) 3.0 (2006):

unwonted
    adj 1: out of the ordinary; "an unwonted softness in her face"

Moby Thesaurus II by Grady Ward, 1.0:

48 Moby Thesaurus words for "unwonted":
   a stranger to, abnormal, atypical, breakaway, disaccustomed,
   extraordinary, ignorant, inexperienced, infrequent, irregular,
   new to, odd, offbeat, peculiar, rare, recherche, rusty, singular,
   strange, sui generis, unaccustomed, unacquainted with, uncommon,
   unconventional, unconversant with, uncustomary, undreamed-of,
   unexpected, unfamiliar, unfamiliar with, unhabituated, unhardened,
   unheard-of, unimaginable, uninured, unique, unordinary, unorthodox,
   unpracticed, unprecedented, unseasoned, unthinkable, unthought-of,
   untrained, unused, unused to, unusual, weaned